The present invention relates to a permanent magnet rotor and in particular relates to a brushless silicon steel rotor using plug-in type arc-shaped permanent magnets, capable of reducing magnetic flux leakage.
The direct current brushless rotor using plug-in type arc-shaped permanent magnets can usually be manufactured with relative ease. To improve space utilization, the gap between two magnets is reduced to the degree that the manufacturing process would allow, resulting in unwanted drawback of magnetic flux leakage. Usually, the shorter the gap, the more serious the magnetic flux leakage. The problems caused by magnetic flux leakage are two-folds: (1) decreasing effective torque and reducing motor efficiency and (2) increasing cogging torque and lowering start capability, as well as causing vibration and noise and comprising overall motor performance.
FIG. 1 shows a 3-dimensional perspective of a brushless permanent magnet direct current rotor 10 using plug-in type arc-shaped permanent magnets in accordance with an embodiment of the prior art, wherein a rotary iron core is formed by stacking a plurality of round steel plates 12, each steel plate 12 having, on its circumference, a plurality of arc-shaped openings 121. A plurality of arc-shaped permanent magnets of alternating poles is so arranged that each permanent magnet 13 be provided in a corresponding opening 121. Said round steel plates 12 are secured together to form a solid piece by pins, screw bolts or rivets through rivet holes 122. The outer perimeter comers of two adjacent permanent magnets 13, have the highest concentration of magnetic flux. As previously stated, when the outer perimeter comers of two adjacent permanent magnets 13, get too close, conventional permanent magnet rotor 10 as shown in FIG. 1 is prone to magnetic flux leakage. Such magnetic flux leakage affects motor efficiency and start capability, produces vibration and noise, and lowers overall motor performance.
Later inventions suggest round-cornered permanent magnets for improving permanent magnet rotor 20. As shown in FIG. 2, the quest for reduced magnetic flux leakage involves adopting round-cornered design for outer perimeter corners 231 of two adjacent permanent magnets 13 so as to create a near triangle-shaped region 24. Instead of leaving the triangle-shaped region 24 an open space, the individual round steel plate 22 now fills said region 24. Since round steel plates 22 are of magnetic material such as silicon steel, magnetic flux leakage remains a problem to be resolved.
U.S. Pat. No. 6,087,752 discloses a recessed steel plate design aimed for improving magnetic flux leakage in permanent magnet rotor. However, the permanent magnets are bar-shaped and being oriented in radial direction. The magnetic leakage problem continues as a result.
Prior arts, U.S. Pat. No. 5,581,140 and U.S. Pat. No. 4,954,736 are related prior arts with similar disadvantages shared by the embodiment of FIG. 2.
An object of the present invention is to provide a permanent magnet rotor structure using plug-in type arc-shaped permanent magnets, capable of reducing magnetic flux leakage and elevating overall motor performance.
To that end, the present invention reveals a permanent magnet rotor, comprising a rotary iron core formed by stacking a plurality of round steel plates, and a plurality of arc-shaped permanent magnets. Each round steel plate has, on its circumference, a plurality of individual arc-shaped openings separated from one another. A permanent magnet of suitable size and shape is provided in an arc-shaped opening. Said permanent magnets of alternating poles are so arranged that each permanent magnet be provided in a corresponding opening. The characteristics of the present invention include round-cornered design by removing sharp cornered areas in outer perimeter corners of two adjacent permanent magnets 13 so as to help form open triangle-shaped regions not fully occupied by solid steel plates, said open triangle-shaped regions being formed by removing portions of or creating holes in said steel plates. The magnetic flux is thus reduced and the motor efficiency elevated.
In one aspect of the present invention, said steel plates having portions removed are provided by creating v-shaped grooves on the outer wall of steel plates so that the tip of v-shaped grooves points the round-cornered areas.
In another aspect of the present invention, said steel plates having holes created are provided by generating triangle-shaped channels on the portions of steel plates opposite round-cornered areas.
In yet another aspect of the present invention, coordination of orientation for steel plates is achieved by marking the same depression on the same location of individual steel plates, each plate having a depression on one side and a corresponding elevation on the opposite side thereof, and stacking a plurality of said steel plates so that the depressions of individual steel plates fit one upon another.
The following Description and Designation of Drawings are provided in order to help understand the features and content of the present invention.